This invention relates to several new pyruvate compounds and methods for resuscitation and reanimation of mammals, especially humans, before, during and after, e.g., (1) mesenteric ischemia, mesenteric thrombus or mesenteric venous occlusion; (2) aortic aneurism repair, coronary artery bypass, surgical treatment of arterial occlusion of limbs; (3) hemorrhagic shock, resulting from either penetrating and blunt trauma; and (4) preservation and transplantation of organs. Ischemia is defined herein as the interruption of oxygen supply, via the blood, to an organ or to part of an organ. Examples of ischemic events include (i) myocardial, cerebral, or intestinal infarction following obstruction of a branch of a coronary, cerebral, or mesenteric artery, and (ii) removal and storage of an organ prior to transplantation. In the case of myocardial infarction, prompt restoration of blood flow to the ischemic myocardium, i.e. coronary reperfusion, is a key component of the treatment. This is because mortality is directly related to infarct size (tissue necrosed) which is related to the severity and duration of the ischemic event. The consequences of hemorrhagic shock are similar to those of ischemia, although the causative event is not an interruption of blood flow but rather the event of massive blood loss itself which causes deprivation of the oxygen supply.
Notwithstanding the need to supply an organ cut-off from a normal blood supply with oxygen, it has been found that reperfusion injury may occur upon restoration of blood flow. This results from the production of reactive oxygen species (ROS), namely, hydrogen peroxide, hydroxyl radicals and superoxide radicals, among others, which are formed from both extracellular and intracellular sources. ROS are highly reactive species that, under normal conditions, are scavenged by endogenous defense mechanisms. However, under conditions of post-ischemic oxidative stress, ROS interact with a variety of cellular components, causing peroxidation of lipids, denaturation of proteins, and interstitial matrix damage and resulting in increase of membrane permeability and release of tissue enzymes.
In an attempt to minimize these undesirable side effects of perfusion in the treatment of ischemia and also of shock, researchers have demonstrated the utility of various antioxidants in the reperfusion process.
Banda et al. (1996), together with Kurose et al. (1997), suggested the use of an inhibitor of ROS production to protect the reperfused myocardium and the use of agents and inhibitors that reduce ROS levels. In a similar context, desiring to provide more efficient resuscitation, researchers have demonstrated the additive utility of incorporating an antioxidant and a beneficial metabolic fuel into the reperfusion regimen. Salahudeen et al. (1991) used solutions of pyruvate, an ROS scavenger and a metabolically important precursor fuel for gluconeogenesis, to protect against hydrogen peroxide induced acute renal failure. Cicalese et al. (1996) found that pretreatment with intraluminal pyruvate ameliorates post ischemic small bowel injury while Crestanello et al. (1998), DeBoer et al. (1993), and O'Donnell-Tormey et al. (1987) have substantiated this finding by examining the ameliorative effects of both endogenously secreted pyruvate and exogenously added material in the reperfusion and subsequent function of organ and tissue preparations subjected to ischemia and simulated shock. Varma et al. (1998), similarly, have shown that in a cultured lens system, after exposure of the cultured lens to free radical oxidant stress, pyruvate and its esters have certain cytoprotecting and restorative effects.
In a further effort directed to protecting reperfused heart tissue, U.S. Pat. No. 5,075,210, herein incorporated by reference, discloses a process for reperfusing a heart for transplantation. The patent discloses a cardioplegic solution containing sodium chloride, potassium chloride, calcium chloride, sodium bicarbonate, sodium EDTA, magnesium chloride, sodium pyruvate and a protein.
U.S. Pat. No. 5,294,641, herein incorporated by reference, is directed to the use of pyruvate to prevent the adverse effects of ischemia. The pyruvate is administered prior to a surgical procedure to increase a patient's cardiac output and heart stroke volume. The pyruvate is administered as a calcium or sodium salt. The pyruvate can alternatively be an amide of pyruvic acid such as ethylamino pyruvate. Similarly, U.S. Pat. No. 5,508,308, herein incorporated by reference, discloses the use of pyruvyl glycine to treat reperfusion injury following myocardial infarction.
U.S. Pat. No. 4,988,515 and 5,705,210, herein incorporated by reference, use pyruvate salts in cardidoplegic solutions and in preservation solutions for the heart before transplantation. U.S. Pat. No. 4,970,143, herein incorporated by reference, discloses the use of acetoacetate for preserving tissue, including addition of the pyruvate to the preservation solution.
U.S. Pat. No. 5,100,677 herein incorporated by reference, discloses the composition of various parenteral solutions. Of interest is a recommendation to include pyruvate anions (apparently from metal salts) in intravenous solutions.
U.S. Pat. No. 5,798,388, herein incorporated by reference, further describes the utility of pyruvate salts and of various complex derivatives, such as amides, for the treatment of ROS in the context of airway inflammation. The patent discloses a pyruvate compound in the form of a covalently linked pyruvoyl-amino acid. By utilizing this type of a pyruvate delivery system, the negative effect of pyruvate salt is avoided. However, administration of large amounts of pyruvate-amino acid may result in nitrogen overload which could harm patients with liver and/or kidney pathology.
In a similar context and based on a similar rationale for pyruvate delivery, U.S. Pat. No. 5,876,916 pertains to the utility of pyruvate thiolesters and polyol esters for the treatment or prevention of reperfusion injury following ischemia, diabetic effects, cholesterol levels, injured organs, ethanol intoxication or as a foodstuff; and U.S. Pat. Nos. 5,633,285; 5,648,380; 5,652,274; and 5,658,957, each herein incorporated by reference, disclose various compositions, salts, prodrugs and derivatives of pyruvate in mixtures with other antioxidants, fatty acids as anti-inflammatory and immunostimulating wound healing compositions. However, administration of large amounts of complex pyruvate-amino acid and other pro-drug derivatives requiring enzymatic hydrolysis prior to liberation of their antioxidant effects may result in nitrogen and/or other xenobiotic overload, which could harm patients directly, interfere with normal detoxifying processes, or cause toxic effects through by-products of limited shelf-life.
Notwithstanding the acceptance of pyruvate as an effective component of a reperfusion solution or other varied applications, pyruvic acid is a strong and unstable acid which cannot be infused as such. On standing in solution, pyruvic acid and its salts at various pH values, including in the physiological range, are known to form both a stable hydrate and a dimer (para-pyruvate), neither of which react with ROS as antioxidants and both of which are known inhibitors of pyruvate utilization as a metabolic fuel, thereby abrogating any of the beneficial effects which might have accrued from pyruvate administration in accordance with the prior art just described.
Furthermore, it has been recognized that traditional pharmacological pyruvate compounds, such as salts of pyruvic acid, are not particularly physiologically suitable. For example, these compounds lead to the accumulation of large concentrations of ions (e.g., calcium or sodium) in the patient's body fluids. Similarly, amino acid compounds containing pyruvate can lead to excessive nitrogen loads. It has also been proposed to infuse pyruvylglycine, the amide function of which is presumably hydrolyzed in plasma and/or tissues, thus liberating pyruvate.
However, at the high rates of pyruvoylglycine infusion required to achieve 1 mM pyruvate in plasma, the glycine load may be harmful to patients suffering from hepatic or renal pathologies. Also, flooding plasma with glycine may interfere with the transport of some amino acids across the blood-brain barrier. Accordingly, while potentially suitable to organ preservation, these pyruvate compounds are less suited to treating an organ in vivo, and it is recognized that a need exists to provide a pyruvate delivery compound that is more physiologically acceptable.
There is also a recognized need to provide a pyruvate delivery system that is cost effective, simple, and devoid of opportunities for contamination because of 1) limited shelf-life, 2) complexity of formulation, 3) reactivity and co-reactivity with excipients and other formulation materials, 4) adverse biochemical reactivity during transport, translocation, and uptake into tissues, and 5) the requirement for metabolic activation via enzymatic hydrolysis by amidases or peptidases. Therefore, it would be desirable to have available an alternate physiologically compatible therapeutic pyruvate compound.